Well, here we go again. The debate continues: should one resistance train with a fast or slow velocity of movement? I thought this was resolved years ago, but obviously it was not. It is time we take a look at the evidence-based research – and add a dose of common sense – to simplify this issue so we can focus on more important training variables.
Fast and slow are both relative terms. The tortoise and the hare represent a general example of the extreme ends of the velocity-of-movement continuum: compared to each other, one moves S-L-O-W and the other lightening fast. However, when it comes to resistance training, it is not that simple since we are using RESISTANCE! Too many factors come into play (muscle fiber type, limb length, skill, one’s conscious effort, etc.). In addition, there is a subjective nature in quantifying what is fast and what is slow. How fast and how slow when recommending an appropriate velocity to optimize the desired training stimulus? How is that accurately measured?
Let’s take a look at a recent study entitled Difference in Kinematics and Kinetics Between High- and Low-Velocity Resistance Loading Equated by Volume: Implications for Hypertrophy Training. In my opinion, it was another study that further clouds the velocity-of-movement issue. But hang on; I will offer a simple explanation to all of this later on in plain English.
The goal of the study was to determine if two training loads of equal training volume – 35% and 70% of a 1 repetition maximum (1RM) – differed in terms of their session kinematics and kinetics (kinematics = aspect of motion apart from considerations of mass and force; kinetics = effect of forces upon the motions of material bodies).
Twelve subjects were used in this acute, randomized, and within-subject crossover design study.
Two bouts of a half-squat exercise were performed one week apart, one utilizing a high load-low velocity (HLLV = 3 sets of 12 reps at 70% 1RM) and the other a low-load high-velocity (LLHV = 6 sets of 12 reps at 35% 1RM).
Time under tension, average force, peak force, average power, peak power, total work, and total impulse were calculated and compared between the two loads for the eccentric and concentric phases.
For average eccentric and concentric single repetition values, significantly greater peak power outputs were associated with the LLHV loading, whereas significantly greater values were associated with the HLLV condition for most of the other variables.
In terms of total session kinematics and kinetics, the LLHV protocol resulted in significantly greater eccentric and concentric time under tension, peak force, average power, peak power, and total work. The only variable that was significantly greater for the HLLV protocol than for the LLHV protocol was total impulse.
Based on their results, they concluded that it seems the LLHV protocol may offer an equal if not better training stimulus for muscular adaptation than the HLLV protocol, because of the greater time under tension, power, force, and work output when the total volume of the exercise is equated.
So, what do we make of this study? Let’s take a look at some time-proven facts and the reality of life on planet Earth:
- Any time resistance is added to an exercise movement that is attempted as fast as possible, it slows the velocity (all other factors being equal). Think about it: even the slightest amount of resistance (as compared to no resistance) creates some drag due to gravitational pull. The heavier it is, the slower. The lighter it is, the faster. We cannot escape that.
- The long-standing Henneman’s Principle of muscle fiber recruitment governs all displays of muscular contraction: the lower the demand (i.e., light resistance, faster velocity) = a lesser recruitment of fibers. The higher the demand (i.e., heavy resistance, naturally slower velocity) = a greater recruitment of fibers. This is undisputable.
- Believe it or not, the heavy/slower velocity scenario actually recruits the larger, higher-threshold “fast” muscle fibers. It is commonly thought that to work the “fast twitch” muscle one must move quickly.
This is exactly the point where many fall off a cliff.
The terms “fast” and “slow” fibers refer the time to fatigue, not velocity of contraction (the difference between contraction speed of fast vs. slow fibers is separated by milliseconds!). So, higher-demand fast fibers fatigue “faster” than lower-demand fibers, which explains why humans cannot sprint for a long time nor lift heavy weights for a high number of repetitions. It also demonstrates why one can walk on a treadmill for an hour: this low-demand activity only recruits a small percentage of slow-to-fatigue muscle fibers. Their endurance capacity allows for this activity to be sustained without the use of higher-demand fibers.
These researchers also stated that although it is commonly believed a high load is necessary for muscle hypertrophy (growth), it is possible a low load with a high velocity results in greater kinematics and kinetics than does a high load with slow velocity. How greater kinematics and kinetics positively affect muscle growth was not elaborated on.
Here is the bottom line for all of you wanting to know “what resistance training speed should I use to grow muscle?”
- Stimulate the greatest number of muscle fibers. Maximum muscle hypertrophy requires the stimulation of the greatest number of muscle fibers (all other factors being equal). That is common sense. They key to effective hypertrophy-type resistance training are protocols that recruit and overload AS MANY FIBERS POSSIBLE – both fast and slow.
- Maximally fatigue muscle tissue. The velocity of movement is not a critical aspect in the pursuit of hypertrophy. The emphasis should be on creating muscle fatigue. Light or heavy, fast velocity or slow, one should exercise to the point of volitional muscular fatigue where no further repetitions are possible. This creates an overload on a larger “pool” of muscle fibers.
- Exercise safely. Forces that exceed the structural integrity of joint tendons and ligaments increase the probability of injury.
Common sense dictates that high-speed movements and ultra-heavy resistances can do this. Therefore, two important suggestions:
- You don’t need super heavy resistances (creates greater joint stress).
- Slow the movement velocity (moving too fast creates too much momentum which can result in excessive joint/muscle stress and decrease in muscle fiber recruitment).
Take home message: If you want to get stronger, increase muscle mass, and do it with minimal risk of injury – SLOW IT DOWN!